2004/10/26 by C. Fechner, Fechner, C., D. Reimers +1
Engineering · Mathematics · Physics and Astronomy · #Artifact (error) #Astronomical Observations and Instrumentation #Astronomy #Astrophysics #Astrophysics (astro-ph) #Calibration and Measurement Techniques #Computational physics #Doppler effect #FOS: Physical sciences #Geometry #Line (geometry) #Lyman-alpha forest #Mathematics #Noise (video) #Optics #Physics #Solar and Space Plasma Dynamics #Spectral line #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0410622
published in arXiv (Cornell University) (Cornell University) · 3 pages, 1 figure, to appear in Astrophysics in the Far Ultraviolet: Five Years of Discovery with FUSE, ASP Conf. series, eds. G. Sonneborn, W. Moos & B.-G. Andersson
arxiv created 2004/10/26 · openalex publication_date 2004/10/26 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/06
Using an artificial HI Lyman alpha spectrum we simulate the corresponding HeII forest with fixed values of eta and a Doppler parameter consisting of a thermal and a turbulent part. In addition metal lines with line strengths and line density as expected in the case of HS 1700+6416 are superimposed. FUSE-like noise is added. The analysis of the simulated spectra in terms of Doppler profiles recovers the input eta = N(HeII)/N(HI) with a scatter by a factor of 10. About 10 % have significantly lower eta-values for various reasons. The majority of the extremely high eta-values (up to 1000) are evidently caused by metal lines. We conclude that part of the scatter in eta of previous analyses of the HeII forest in HE 2347-4342 can be regarded as an artifact. However, we confirm that the correlation between small column densities (in voids) and high eta-values is not a methodical artifact and appears to be a true phenomenon.